Systems for providing positional and navigational information are known in the art. Typically, these systems utilise signals derived from a Global Positioning System (GPS) such as the NAVSTAR system.
Navstar was developed to provide accurate position, velocity, and time information in any environmental conditions. The system includes twenty-four satellites arranged in six orbital planes such that the satellites orbit the planet in circular orbits with a twelve hour period. The satellite orbits are arranged such that at least four satellites are in "view" (i.e. not obscured by the curvature of the planet) from any position on the planet.
Each user module receives periodically transmitted signals from four satellites. The user unit computes a range to each satellite based upon the known time of receipt of the signal, and a predicted time of transmission of the signal from the satellite. GPS systems commonly have two standards of operation; a military standard and a civilian standard. Systems operating according to the military standard provide a positional accuracy of 16 meters, a velocity accuracy of 0.1 meters per second, and a time accuracy to 100 nanoseconds. However, the signals transmitted by the satellites according to the military standard are encrypted to prevent unauthorised access. Comparably, systems operating according to the civilian standard provide a positional accuracy of 100 meters.
Vehicle navigational systems are well known in the art. For example, European Patent Application No. EP-A-0,542,331 discloses a vehicle navigational device for directing a vehicle along a predetermined route. The device utilises GPS positional data displayed on a display unit within the vehicle
The "Route Planner" system manufactured by TECmobility.TM. a subsidiary of Magneti Marelli is a navigational device that provides positional information of a vehicle relative to a map, together with a route planning capability. The position of the vehicle is estimated using positional data from signals received from GPS satellites. The actual position of the vehicle is then corrected by algorithms that relate the positional data computed from received GPS signals to a corresponding position on map of the current location of the vehicle stored on a CD-ROM.
The route planning function calculates the best route between the current vehicle location and a user selected destination. The system is capable of recalculating the route should the user deviate from the predetermined route due to adverse traffic conditions etc. The system is further capable of receiving data relating to the conditions on the predetermined route, and recalculating the route in accordance with the received traffic conditions etc.
However, although the system is capable of receiving data for causing the recalculation of the predetermined route due to adverse traffic conditions, the system is not capable of proactively recalculating the route due to the planned route calculations of other users of the system. For example, a user may be provided with a predetermined route which takes account of the current traffic conditions, but the system takes no account of the predicted travel conditions on the route within the travel period of the user. Consequently, although the selected route may be determined in accordance with the traffic conditions at the time of route determination, the predetermined route may be less appropriate when considering the intentions of other road users.